Tests on mortars

To study the influence of MSWI fly ash on the short-term and middle-term properties of mortars, certain performance characteristics of mortars containing increasing levels of MSWI fly ash were studied. The compositions of the mortars all derive from the composition of standardized mortar as specified in the NF EN 196-1 standard [5]. The fly ash was incorporated in the mortars in place of a fraction of the sand, with all the other components remaining unchanged in relation to the reference mortar. Only cement C1 has been used for this part of the study. Table 2 shows the compositions of the five mortars used.

To study the influence of the soluble fraction of MSWI fly ash, 65 g of ash were washed in 325 g of water for 3 min. Three compositions were studied: mortar M10 (identical to that shown in Table 2), mortar M'10 in which MSWI fly ash was replaced by washed ash, and mortar M'0 in which the mixing mortar water was replaced by an ash wash solution.

The mortar blending times and rates complied with the NF P15-403 standard [7] in all the tests carried out. Blending times specified in this standard are in fact longer than those specified in the NF EN 196-1 standard [5], and were a factor in limiting the segregation observed during preliminary tests carried out with a shorter mixing time.

The flow times recorded using the LCPC mortar "workability meter" were analyzed in accordance with NF P18- 452 standard [8] for each composition. The initial and final setting times of the M0, M5, M10, M15 and M20 mortars were measured with the Vicat needle in accordance with the NF P 18-356 standard [9]. 40 mm x 40 mm x 160 mm test pieces were placed on the impact test bench in accordance with NF EN 196-1 standard [5] to determine the mechanical strength of M0, M5, M10, M15 and M20 mortars. After setting-up, the mortars were stored in sealed bags until removed from the mold (approximately 3 d). After removal, the test pieces were once again placed in sealed bags and kept at a temperature of 20 ºC until the tests were carried out. The ultimate 3-point bending tensile strength and compressive strength were determined in accordance with NF EN 196-1 standard [5] on the following days: 7, 28, 90 and 565. The compressive strength of the M10 (10 % ash), M'10 (10 % washed ash) and M'0 (0 % ash and washwater) mortars after 28 d were also determined. In this case, the test pieces were kept at 20 ºC and 50 % relative humidity.

Mass and size variations of the M0, M10 and M20 mortars were also determined after (3, 7, 14, 21, 28 and 35) d. These tests were carried out on test pieces of 20 mm x 40 mm x 160 mm for testing size variations, and 40 mm x 40 mm x 160 mm for mass variations. The test pieces were kept throughout the duration of the tests at 20 ºC and 50 % relative humidity.